1. Field of the Invention
The present invention relates to plasma sources, and more particularly to induction plasma sources for integrated circuit fabrication.
2. Description of Related Art
Plasma etching is useful in many fields, but particularly in the field of microelectronic fabrication. Microelectronic fabrication of integrated circuits requires mass replication of tightly controlled, submicron-sized features in a variety of materials, as well as selective removal of material without causing damage to sensitive structures and remaining materials. Illustrative application of plasma etching to microelectronic fabrication of integrated circuits includes ion sputter cleaning, dielectric gap filling involving simultaneous chemical vapor deposition ("CVD") and etch, chemical blanket etchback without resist, and chemical pattern etch with resist.
Various plasma source methods and geometric designs for reactors are known for use in plasma deposition and etching. For example, electron cyclotron resonance ("ECR") sources are available from Applied Science and Technology, Inc., Woburn, Mass. and from the WAVEMAT Corporation, Plymouth, Mass. Also, wafer cleaning and etching processes have commonly been done with equipment using various cylindrical shaped quartz vessels of various diameters having induction windings of various pitches, either constant or variable, as well as with flat spiral induction windings mounted above the dielectric chamber top plate. Radio frequency ("rf") diode and triode configurations are also known in which the wafer electrode and possibly other electrodes are powered at 13.56 MHz to produce the plasma.
Physical sputtering, one of several plasma etching mechanisms, involves the removal of material by energetic ions, which cross the sheath and transfer energy and momentum to the material being etched. As implemented on a great many of the prior art inductively coupled cavity and/or diode and triode machines, physical sputtering suffers from a number of disadvantages, including low material removal rate, poor etch uniformity due to poor ion current uniformity, and electrical damage to the substrate from ion bombardment and implantation due to high ion energies. The ECR sources provide improved performance, but with considerably greater complexity than induction-type sources.
Hence, a need continues for plasma source systems that are able to provide good ion density to achieve high etch rates, ion current uniformity to achieve uniform removal of material over large diameter substrates, and operational stability at low pressure to achieve a more uniform ion distribution in the plasma and better directionality of ions in high aspect ratio structures, all in a generally simple machine implementation.